SINGAPORE, May 13 (Reuters) - Asian oil buyers are bracing for surging prices in the spot crude market as global supplies have tightened after stringent U.S. sanctions on producers, disruptions of Russian oil flows in Europe and maintenance at oilfields in the Atlantic Basin and Asia.

Buyers have already paid a premium of $6 a barrel to benchmark Dubai quotes for Russia’s Sokol crude for July loading, the highest premium since 2014. The premium for July-loading Oman crude futures to Dubai is at $3.46 a barrel, the most for this time of year in four years.

The surging premiums are the result of the confluence of several factors limiting global supply.

Asian buyers were already competing with U.S. refiners for the same pool of resources after the United States imposed sanctions on supplies from Venezuela, forcing buyers to turn to the Middle East, Africa and Latin America for replacements.

Oman prices are jumping as the U.S. stopped granting waivers to Iranian sanctions that have curtailed exports of the so-called heavy crudes that it produces.

Asia’s demand for Russian and Middle Eastern light grades such as Sokol and Murban strengthened after arbitrage supplies from the Atlantic Basin and the United States fell.

The contamination of Russian Urals crude on pipelines into Europe and the longer-than-expected closure of the North Sea’s Oseberg field have caused benchmark Brent’s premium to Dubai to surge above $3 a barrel, making Atlantic Basin oil more expensive for Asian buyers.

Angolan crudes were already selling at all-time high premiums as exports have dropped due to field maintenance while some Nigerian production were under force majeure.

Cargoes of Middle East Murban crude are at premiums of about 75 cents a barrel for July loading, the most since 2015, according to Refinitiv data, while two trade sources said premiums may have risen above $1 a barrel this week.

Refiners are expecting to make up the supply shortfall from Saudi Arabia, though the country is likely to keep its exports below 7 million barrels per day to avoid a price crash like the one at the end of 2018.

Rising prices have pushed up costs for Asian buyers and could weigh on regional refining margins that are at their lowest in five years for this time of year. DUB-SIN-REF

“With a tight supply side picture, Saudi Arabia is unlikely to repeat its mistakes from 2018 and with new refineries in the region ramping up, Asian refiners will need to pay up for barrels,” said Virendra Chauhan, a Singapore-based oil analyst at consultancy Energy Aspects.

“We have heavy oilfield maintenance in Norway and West Africa across May and June,” said Chauhan.

“All of these factors have been compounded by the Russia contamination issue.”

Several European buyers halted oil imports from Russia via the Druzhba pipeline after finding contaminants that could damage refinery equipment.

In Asia, Malaysia’s Kimanis crude exports will also fall sharply in July because of field maintenance.

Asian refiners are currently re-running computer programmes that determine which crude grades are economical to buy as they factor in higher spot prices, while also considering whether to trim crude throughput, said two sources at different North Asian refineries.

“Refineries which are running at maximum capacities may instead run a little lower,” one of the sources said.